Y zeolite dealuminated

An amorphous component such as silica-alumina is added to the catalyst, for a sort of pre-cracking of the large molecules (greater than about C25), which cannot enter the zeolite pores. The smaller fragments may then react in the zeolite. Middle distillates maximum yield is achieved by the use of dealuminated Y zeolites. 

Liquid-phase breakthrough experiments were also developed in order to characterize mesopores. The principle of the methodology relied on the analysis of the diffusion and adsorption of molecular probes with various molecular dimensions and adsorption strength. The relative proportion of occluded and accessible mesopores in the studied dealuminated Y zeolite could then be estimated. To allow this estimation, it is necessary to use molecular probes that can or cannot penetrate into the microporosity of the Y zeolite (see Figure 2). 

It was found that more than 70 % of the mesopore volume of the highly dealuminated Y zeolite was externally accessible [7]. Interestingly these results are in accordance with... 

These data clearly indicate that the NiMCM-36 catalyst exhibits very interesting properties for ethylene oligomerization, by comparison with the microporous NiMCM-22 zeolite at both reaction temperatures (70 and 150°C, respectively). Compared with other catalysts, the NiMCM-36 behaviour is intermediate between Ni-exchanged dealuminated Y zeolite and Ni-exchanged mesoporous materials. Taking into account that the amount of Ni2+ sites is near the same for all samples (Table 1), in order to explain these differences in catalytic behaviors, two mains categories of properties could be considered (i) the concentration and strength of acid and nickel sites and (ii) the diffusional properties (determined by the size and the architecture of pores). 

The microwave technique has also been found to be a potential method for the preparation of the catalysts containing highly dispersed metal compounds on high-porosity materials. The process is based on thermal dispersion of active species, facilitated by microwave energy, into the internal pore surface of a microporous support. Dealuminated Y zeolite-supported CuO and CuCl sorbents were prepared by this method and used for S02 removal and industrial gas separation, respectively [5], The results demonstrated the effective preparation of supported sorbents by micro-wave heating. The method was simple, fast, and energy-efficient, because the synthesis of both sorbents required a much lower temperature and much less time compared with conventional thermal dispersion. 

X-ray studies carried out by Gallezot et al. (46) on a 53 percent EDTA-dealuminated Y zeolite, have shown that the aluminum extraction does not leave any vacancies in the framework after calcination at 400°C in flowing, dry oxygen and nitrogen (46). It was suggested that a local re-crystall-ization of the framework occurs even in the absence of steam. The silica necessary for the process presumably originates in the destroyed surface layers of the crystallite and diffuses into its interior. 

Sorption. Lohse et al. (36,47,48) have studied the sorption properties of acid-dealuminated Y zeolites that contain about 99% SiC, and compared them with those of the... 

The infrared spectra of EDTA-dealuminated Y zeolites show bands in the OH stretching region similar to those encountered in HY zeolites at about 3750, 3640 and 3540 cm (50,54). However, the OH groups responsible for the 3640 and 3540 cm bands in the spectra of the aluminum-deficient zeolites... 

Pyridine sorption studies on EDTA-dealuminated Y zeolites at various temperatures (54,58), as well as measurements of differential heats of adsorption of ammonia on aluminum-deficient Y zeolites (57,59) have led to the conclusion that aluminum-deficient Y zeolites have stronger acid sites than the parent zeolite. 

Ab initio methods, 147-49 Acetate ion, decomposition, 135 Acetylene, interaction with palladium, tunneling spectroscopy, 435,437f Acid-dealuminated Y zeolites catalytical properties, 183 sorption, 175-78 Acid sites, on zeolites, 254 acidification effects, 266 Acoustic ringing, in NMR, elimination, 386 Active sites, nature, 104 Activity measurements, Co-Mo catalysts, 74 Adsorbed molecules,... 

Kulprathipanja, S. (1991) Process for separabng glucose and mannose with dealuminated Y zeolites. U.S. Patent 5,000,794. 

Cruz, ).M., Corma, A., and Eornes, V., Framework (1989) Framework and extra-framework aluminium distribution in (NHdjSiFs-dealuminated Y zeolites relevance to cracking catalysts. Appl. Catal, 50, 287. 

Likewise thioacetals have been prepared in yields between 60 to >99% by treatment of aldehydes or ketones with 1,2-ethanethiol in the presence of Zeolite HSZ-360, a dealuminated Y-Zeolite [101]. Many other functional groups like al-kenes, tetrahydropyranyl and nitriles are tolerated under the mild reaction conditions. 

Chemically dealuminated Y zeolite was prepared starting from NHa exchanged Y (2.5 Si/Al ratio) using the procedure of Skeels... 

Zeolites are crystalline aluminosilicates with a regular pore structure. These materials have been used in major catalytic processes for a number of years. The application using the largest quantities of zeolites is FCC [102]. The zeolites with significant cracking activity are dealuminated Y zeolites that exhibit greatly increased hydrothermal stability, and are accordingly called ultrastable Y zeolites (USY), ZSM-5 (alternatively known as MFI), mordenite, offretite, and erionite [103]. 

In 1994, Laketic et al. investigated for the first time the hydrolysis of sucrose over dealuminated-Y-zeolites with different Si/Al ratio (27, 55, 110). The best activity was observed with the highest dealuminated zeolite (Si/Al = 110, rate constant = 1.28 L moE min at 30°C [32]). As expected, the reaction obeys first order kinetics. Up to 90% conversion was obtained after 9 h of reaction at 70°C. Interestingly, little side-products were formed as the selectivity in glucose was higher than 90%. 

In a previous paper (14) we have shown that by an adequate treatment of steam dealuminated Y zeolites with (NH4)2SiF6 it is possible to remove selectively the EFAL. The physicochemical characterization of these samples shows that the presence of EFAL is the responsible for the formation of superacid sites, as well as for the neutralization of a part of framework hydroxyls. 

A linear dependence with pore diameter is observed. The intermolecular distance, directly dependent on the curvature of the pores, i.e. the average pore diameter, is linearly related to the activation energy for dehydroxylation. Extrapolation to smaller pores suggests activation energies of approximately 100 kJ mol 1 for dehydroxylation of hydroxyl groups in e.g. zeolite channels, if the hydroxyls are of a comparable type. Rees published corresponding activation energies for water desorption in dealuminated Y-zeolites.34... 

Fig. 1. Model of rhodium dicarbonyl complex on dealuminated Y zeolite, as determined by IR and EXAFS spectroscopies and density functional theory. The Rh atom, near the upper center of the figure, has two CO ligands bonded to it, pointing upward, and two oxygen atoms of the zeolite lattice below. An Al atom is located between these two oxygen atoms. The dangling atoms of the cluster model of the zeolite are capped by hydrogen atoms for the calculation (Goellner, Gates, etal., 2000).

Fig. 2. Infrared spectra in the carbonyl stretching region of Y zeolite-supported Rh(CO)2. (A) Complex in NaY zeolite calcined at 200° C. (B) Complex in dealuminated Y zeolite calcined at 120° C. (C) Complex in dealuminated Y zeolite calcined at 300°C (Goellner, Gates, et al, 2000).

Comparison of Structural Parameters Determined by Density Functional Theory and by EXAFS Spectroscopy Characterizing Samples Made from Chemisorption of [Rh(CO)2(acac)] on Dealuminated Y Zeolite (Goellner, Gates et al., 2000) ... 

Miessner, H., Surface-chemistry in a zeolite matrix—Well-defined dinitrogen complexes of rhodium supported on dealuminated Y-zeolite. J. Am. Chem. Soc. 116,11522 (1994). 

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